In certain types of data storage, such as, for example, thermally assisted optical/magnetic data storage, information bits are recorded on a layer of a storage medium at elevated temperatures, and the heated area in the storage medium determines the data bit dimension. In one approach, an electromagnetic wave in the form of light is used to heat the storage medium. To achieve high areal data density, it is preferred to have a high light throughput to an optical spot well below the diffraction limit to heat the storage layer of the medium. Some prior systems have confined the light to a small spot but did not deliver a reasonable amount of optical power to the storage medium.
Thermal or heat assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. Heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability. Heat assisted magnetic recording can be applied to any type of magnetic storage media, including tilted media, longitudinal media, perpendicular media and patterned media.
Heat assisted magnetic recording requires an efficient technique for delivering large amounts of light power to the recording medium confined to spots of, for example, 50 nm or less. Areal density and bit aspect ratio are among the factors which determine this size. Based on previous studies, 1 Th/in2 requires spots of 25 nm. A variety of transducer designs have been proposed and some have been experimentally tested. Among these are metal coated glass fibers and hollow pyramidal structures with metal walls. For all these approaches, confinement of the light depends on an aperture which is fabricated at the end of the structure and gives this kind of transducer the name “aperture probes.” Generally these devices suffer from very low light transmission rendering the devices useless for HAMR recording. For example, tapered and metallized optical fibers have demonstrated light confinement down to approximately 50 nm with a throughput efficiency of 10−6. Pyramidal probes made from anisotropic etching of Si wafers have been designed with throughput efficiencies of 10−4 for similar spot sizes. Although this is the state of the art, it is still about two orders of magnitude too small for HAMR.
Solid immersion lenses (SILs) and solid immersion mirrors (SIMs) have also been proposed for concentrating far field optical energy into small spots. The optical intensity is very high at the focus but the spot size is still determined by the diffraction limit which in turn depends on the refractive index of the material from which the SIL or SIM is made. The smallest spot size which can be achieved with all currently known transparent materials is ˜60 nm, which is too large for HAMR.
A metal pin can be used as a transducer to concentrate optical energy into arbitrarily small areal dimensions. In previously proposed designs that utilize a metal pin located at a focal point, the pin supports a surface plasmon mode which propagates along the pin, and the width of the radiated electric field generated by the surface plasmon mode is proportional to the diameter of the pin. For recording head arrangements that may utilize the transducer with pin configuration, such as a HAMR device, it is preferred that the pin be in the proximity of the write pole such that the maximum magnetic field generated by the write pole overlaps with the maximum thermal gradient so as to write sharp magnetic transients. However, it has been determined that the pin being in close proximity to the write pole may result in the surface plasmon excitation of the pin being quenched which results in the light delivery efficiency decreasing. In addition, light condensation of the device depends on the gap distance between the write pole and the pin which requires an alignment tolerance of approximately 1-2 nanometers making fabrication of the device more difficult.
There is a need for transducers that can provide a reduced spot size, increased throughput efficiencies, and simplification of manufacturing requirements.
There is also a need for new and improved optical transducer configurations capable of providing the necessary high intensities for generating intense optical spots with sufficiently small sizes to meet the demands of applications which require such optical spots.
There is further identified a need for improved optical transducers that overcome limitations, disadvantages, or shortcomings of known optical transducers.